RE: illegal copies

Ok, is there a list somewhere of companies who do make/distribute bootleg
copies so that we unsuspecting librarians can avoid purchasing these items?
I know from previous posts to avoid Madacy, but obviously, there are others.
How can we tell? Is Amazon able to tell - or do they just take the word of
whoever is providing the product? I know that price is sometimes a sign -
but not always. What can we look for?